1. Field of the Invention
This invention generally relates to a communication apparatus which uses an analog transmission line, such as the public telephone network, for transmission of data, and, in particular, to a facsimile machine whose signal level can be adjusted remotely.
2. Description of the Prior Art
A communication apparatus, such as a facsimile machine, uses the public telephone network, which is an analog transmission network, for communication of data between two stations. In such a communication apparatus, it is necessary to supply a signal having a level corresponding to a loss of the network to which connection is established. For example, if a signal output from a transmitter has a signal level which is relatively small as compared with the network loss, a receiver cannot receive a signal of sufficient level from the transmitter through the network, so that a proper data communication cannot be carried out. For this reason, in a prior art facsimile machine, a plurality of terminals for setting the level of a signal to be output into the network are provided, and the signal output level is adjusted by using a jumper line or the like for the terminals. However, in such a prior art structure, a skilled service person is required for adjusting the signal level, so that it is cumbersome and time consuming.
On the other hand, in the case where a facsimile operates as a receiver, the level of a signal received from a transmitter through the network must be within a predetermined range. That is, if it is allowed to receive a signal very low in level, then even noises may be received by the receiver, which could cause an erroneous receiving operation. Thus, it is necessary to set a lower limit for the level of a signal to be received. In addition, in some countries, it is forbidden to receive signals having certain levels, so that it is necessary to suitably adjust the minimum level for receiving signals in accordance with the regulations of these countries. In this manner, since it is required to change the signal level for reception, a prior art facsimile machine is typically provided with a plurality of terminals for setting the signal level for reception. Thus, by using a jumper line or the like, the signal level for reception can be suitably adjusted. However, with this prior art structure, a skilled service person is required for adjusting the signal level for reception, which is cumbersome and time consuming.